How old is it “to be able to sit without assistance”?

This “to be able to sit without assistance” is the expression on Tokyo Disney Resort official, but does not indicate specifically. So I collected the voices of experienced people.

Generally speaking, how much age of an infant is indicated?

When my child was 7 months, I was asked, “Can he sit without assistance?” I answered outright, “Yes, he can!” Thus, I think the incharged Cast decides ultimately.

They did not allow my near 2-year-old child to ride.

Regardless of age, children who cannot sit down to the last or who can be panic scared during the ride seems to be rejected for safety reason.
Summarizing the above information,”As there are individual differences in children’s growth, the judgment is left to the incharged Cast. In addition, there are also individual differences on the judgment criteria.”
Still, it is better to think that rough guide is “around one and half years old to 2 years old”.